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A rare variation of the biceps brachi muscle

J. Paval, J. G. Mathew Department of Anatomy, Melaka Manipal Medical College, Manipal - 576 104, Karnataka, India

Address for correspondence: Jaijesh Paval, Department of Anatomy, Melaka Manipal Medical College, Manipal - 576 104, Karnataka, India. E-mail: [email protected]

ABSTRACT

Biceps brachii muscle is very variable. Biceps may be composed of one to five heads. Although the variations in the origin are plenty, there are a very few cases reported on the variations in the insertion of the biceps brachii muscle. In this report we present a variant biceps brachii muscle which gives an abnormal muscle fasciculus from its medial side which continues as a narrow tendinous slip and is inserted in to the medial supracondylar ridge of humerus. We discuss in this report, the possible median nerve entrapment due to the presence of such a variation.

KEY WORDS

Biceps brachii, brachial artery, median nerve

INTRODUCTION and was inserted to the radial tuberosity of radius. But some of the fibres from the medial side below the level he most studied and reported upper extremity of the middle of the arm formed a separate muscle bundle nerve entrapment problem is those related with and continued as a narrow tendinous slip [Figure 1]. This T the median nerve. Among these, the most slip soon divided into two- the lateral slip was found common one is the carpal tunnel syndrome. Because superficial to brachial artery and median nerve and the this condition is studied so often, clinicians may be too medial slip was deep to them. The lateral slip crossed eager to assume the presence of carpal tunnel syndrome the cubital fossa, merged with the fascial covering of for any kind of median nerve compressions. In this the flexor carpi ulnaris muscle. The medial slip curved report we discuss a possible median nerve entrapment medially and was attached to the medial supra-condylar in the cubital fossa by an abnormal tendinous slip from ridge of the humerus. the biceps brachii muscle. DISCUSSION CASE REPORT The important variations of biceps brachii reported by During the routine dissection for medical students, we Macalister are as follows;[1] found an abnormal insertion of biceps brachii muscle 1. The muscle may be entirely suppressed unilaterally in a male cadaver. The origin of this biceps 2. The fascial insertion was found to be absent in one brachii was normal. The muscle followed a normal course arm and most of the muscle fibres formed a round tendon 3. Long head arising from the capsular ligament or from

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head may be absent. In the absence of the long head, the tendon may be found arising from the bicipital groove, one of the tubercles, the capsule of the joint or the tendon of pectoralis major. The tendon may be doubled or it may be represented only by the aponeurosis.[4]

The aponeurosis or the lacertus fibrosus which may be doubled may compress the median nerve as found in the pronator syndrome.[5]

The pronator syndrome was first described in 1951 by Seyffarth.[6] He reported 17 patients whom he proposed were suffering from median nerve entrapment as the Figure 1: Flexor compartment of the right arm. A - Extra fasciculus of the biceps brachii, B - Brachial artery, C - Median nerve, D - Tendinous slips from nerve passed through the pronator teres muscle or the the extra fasciculus, E - Lacertus fibrosus flexor digitorum superficialis (FDS) arch. This illustrates the bicipital groove that from the time of the initial description, there has 4. Presence of a slip to the short head from the been ambiguity about the name because it includes more insertion-tendon of pectoralis minor than just compression by the pronator teres. It is now 5. Presence of a third head arising directly from the often referred to as the so-called pronator syndrome brachialis muscle. because it has a common clinical presentation but a “spectrum” of locations of compression. Since 1951, A separate slip from coracobrachialis continuous with there have been numerous reports of patients presenting the short head is described by Wood and Macalister. They with pronator syndrome who have gone on to surgical also described a doubled coracoid head and this decompression with complete recovery. There are four anomalous portion may join the main body of the muscle more commonly described locations of compression: or else it may unite with the normal coracoid head before 1. Ligament of Struthers-an uncommon structure that [7,8] that portion of the biceps joins the long head.[1,2] is rarely believed to cause pronator syndrome. 2. Tight or thickened lacertus fibrosus-often associated Mori described various origins of the third or accessory with brachialis hypertrophy.[9-11] head as follows: In 50 arms there were 10 (20%) arms 3. Fibrous band within the pronator teres-particularly with a third head of the biceps.[3] The origins of these worsened by repeated pro-supination.[9] additional heads were: 4. Proximal edge of FDS- “sublimis arch”—a tight fibrous 1. The distal portion of the deltoid tuberosity, 4 arms, arch between the heads of the FDS.[10] 8%. 2. Near the point of the humeral insertion of The most common areas of compression of the median coracobrachialis, 3 arms, 6% and nerve are at the level of the FDS arch[12] or by the nerve 3. The terminal tendon of pectoralis major, 2 arms, 4%. passing through the pronator teres muscle.[13]

The two other accessory heads are rare and take several In the present case, biceps brachii had an accessory different forms. When fully developed, they arise close muscle fasciculus and this continued as a tendinous slip. together from the neck of the humerus, below the lesser This variation is different from the cases of doubling of tubercle and behind the pectoral tendon to which they lacertus fibrosus. Looking at the close relationship with may be more or less joined. The more lateral of the two the median nerve, this variation can also be considered slips joins the long head of the muscle, whereas the as one of the potential cause of the pronator syndrome. medial joins the short head.[3] The pronator syndrome is much less common than the carpal tunnel syndrome (CTS). It usually presents in the In other instances (Spinner et al), the two heads of the fifth decade and is four times more common in biceps muscle may be totally separate or fused and either women.[13] The symptoms are insidious in onset, with a

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delay in diagnosis ranging from 9 months to 2 years.[8,12,15] the problem before coming to a conclusion about the The patient most commonly complains of aching pain in presence of the popular compressive neuropathies. the proximal forearm and the distal arm. Pain may radiate proximally and is often aggravated by use of the upper REFERENCES limb, especially with resisted forceful pronation or repeated pronation/supination movements.[5,6] As is the 1. Macalister A. Additional observations on muscular anomalies case in CTS, there is usually associated paresthesiae and, in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans Roy Ir possibly, altered sensibility in the radial three and a half Acad Sci 1875;25:1-134. digits,[8] but night awakenings and nocturnal pain are 2. Wood J. On human muscular variations in relation to comparative uncommon- a key symptom to help differentiate from anatomy. J Anat Physiol 1867;1:44-59. CTS. 3. Mori M. Statistics on the musculature of the Japanese. Okajimas Fol Anat Jpn 1964;40:195-300. 4. Spinner RJ, Carmichael SW, Spinner M. Partial median nerve The differential diagnosis of the pronator syndrome is entrapment in the distal arm because of an accessory bicipital extremely important because this entity is relatively aponeurosis. J Hand Surg Am 1991;16:236-44. 5. Lister G. The Hand: Diagnosis and Indications, 3rd ed. Churchill uncommon compared with CTS. In fact, as noted by Livingstone: New York; 1993. p. 291-2. Lister,[5] Symptoms of CTS are very similar to those of 6. Seyffarth H. Primary myoses in the M. Pronator Teres as a pronator syndrome.[5] cause of lesions of the N. Medianus (the pronator syndrome). Acta Psychiatr Neurologica 1951;74:251-4. 7. Laha RK, Lunsford LD, Dujovny M. Lacertus fibrosus [5] Similarities between two syndromes: Pain in wrist and compression of the median nerve: Case report. J Neurosurg forearm regions, weakness of thenar muscles numbness/ 1978;48:838-41. paresthesias of radial three and a half digits. 8. Urbaniak JR. Complications of treatment of carpal tunnel syndrome. Operative Nerve Repair and Reconstruction. JB Lippincott: Philadelphia; 1991. p. 967-79. Differences in two syndromes:[5] No nocturnal pain in 9. Hartz CR, Linscheid RL, Gramse RR. The pronator teres pronator syndrome, negative Tinel’s sign at wrist in syndrome: Compressive neuropathy of the median nerve. J Bone Joint Surg Am 1981;63A:885-90. pronator syndrome, nerve conduction study shows - no 10. Martinelli P, Gabollini AS, Poppi N. Pronator syndrome due to delay at wrist in pronator syndrome. Dysesthesia in palmar thickened bicipital aponeurosis. J Neurol Neurosurg Psychiatr cutaneous distribution is seen in pronator syndrome. 1982;45:181-2. 11. Spinner M, Spencer PS. Nerve compression lesions of the upper extremity: A clinical and experimental review. Clin Orthop Other important differential diagnosis include thoracic 1974;104:46-67. outlet syndrome, proximal brachial plexus neuropathies, 12. Olehnik WK, Manske PR, Szerzinski J. Median nerve cervical radiculopathy and polyneuropathy. The diagnosis compression in the proximal forearm. J Hand Surg Am 1994;19A:121-6. of these conditions is assisted by the use of 13. Goldner JL. Median nerve compression lesions and clinical electrophysiologic investigations.[5] analysis. Bull J Dis 1984;44:199-223. 14. Johnson RK, Spinner M, Shrewsbury MM. Median nerve Considering the entire length of the median nerve, there entrapment syndrome in the proximal forearm. J Hand Surg 1979;4:48-51. are numerous locations that median nerve entrapment 15. Al-Qattan MM, Robertson GA. Pseudo-anterior interosseous nerve may occur. It is very much essential to thoroughly evaluate syndrome: A case report. J Hand Surg Am 1993;18A:440-2.

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